Apparatus for producing a convergent x-ray beam



June 7, 1949. L. K. FREVEL 2,472,745

APPARATUS FOR PRODUCING CONVERGENT X-RAY BEAMS I Filed Sept. 19, 1946 Ifli A MA ill/[11111111,]

IN V EN T 0R. 1. uo o K. Freve/ A TTORNEYS Patented June 7, 1949 l TED Pi This invention'relates' to a 1 device "for produc ing- 'a beam *of- X-rays in the *form ofa-- hollow convergentcone and to apparatus includingthe devicel- Conventional X-ray tubes produce abeam ofdivergent- X-rays, the intensity of which-decreases rapidly as the distance from the =source isincreased." In therapeutic uses, then, in'which deep-"seated tissue is=to betreated-with such-a beam, the surface'tissue; being nearer the source, is unavoidably subjected to X-rays of greater" intensity. dosage ofdeep tissue without serious overex*-=- posure of the surface is thus difiicult. Likewise;

in radiographic work, the divergence of the X-ray beam is'--'sometimes disadvantageous in that 'diffuse shadow patterns are obtained.

It" is accordingly the principal object'of the present invention to avoid these disadvantages by'providing a device for-generating a beam'of- X-rays in'the form-of a hollow cone converging to'a-focus. Another object is to provide appartus for 'using the device in'treatment of deep-seatedtissue:

Basically, the new device comprises aux-ray tube having an-annular or ring-shapedtarget and" a shieldassociated with the tube having one or-* moreannular slits so placed with respectto the target as to restrict the issuingX-rays'to'the" form" of" a" convergent conical beam;

The :apparatus of theinvention; in "a preferred embodiment, may be explained with" reference ft of Fig. 1 mounted for movement in a fixed path about it's'focal point.

The =X-raytube indicated generally as -i3'=is"of' the "hot cathode "high-vacuum type and 1 is in tended for operation" with grounded anode at voltages "ofthe order of '40 to '200 ""kilovolts; A conventional protective'case:surrounds the tube but is not shown in the drawings.

The tube 3 is formed with a hollow steel ienvelope or anode 4"'surmounted"by an annular copper cap 5 soldered to the anode. This cap necks down at its top and is sealed into a conventional tubular glass insulator 6.

A central well I in the insulator terminates in a base 8 over which is fitted a protective metal cap 9. Lead-wires I0 surrounded in part by a Theproblem-of securing; adequate as It cable icovering not-shown; pass down the *we and are sealedin insulating sleeves -I l -which it turn are sealed through the base 8z and"cap 9 'andiii extend into the envelope:

The cathode l structure c isscenteredin th envelope z4 andcontains-a tungstenfilamentii-l i Welded to'the lead wires 10; The-filament is-dis posed inthe -form-of a loop-"of substantial 'diamsv eter transverse-'to the envelope and centered axis-1 ally therein; The filament is surrounded by aa tungsten shield "-whichhas an annular openingzi" I3 dir'ected obliquely-downward. The shield in--- cludes-a transverse top 14 throughwhieh wthee sleeves I I extend; the =top being supportedbya insulating rod l5 mounted in the base-8 Atubi1alar f side-portion I 6 fits =over and exten'ds -d6wnwardly from the top" I4 and flares outwardlyi aift the =1evelofthe -fdlament 12 toform one side the opening I3;1. The othersi'de of the openingw isfdrmedby a correspondingly flared rim of-th'ee bottom piece I I which"ishe1d in place by means of legs I8 attached tothe side -piece I 6.

The envelope 4 is =thickened inwardly at its lower'portion to provide a tubular target supportt I9 in which a passage Zfl fdncooli'rig Water in formedfi Agroove 21 is cut "into the inside -verti-- cal wall of the target-support'ata position suchs'w as to be in the electron pathdefined by thee annular opening I3 in the cathode shield? Ii'ito :this groove is placedan annular target 22 Which as show-nis'coaxial with the filament and spacedaxially-therefrom and has itsX-ray generat-i-ng'q face parallel to-its axis: For-'convenience, thei target is-made of a three-segment tungsten-- ring ofrectangular cross section-which is -pressed-into-s the -groove -2lto be -flush 'w-ith 'the 'wall of tll'e target support I9.

The tube 3 "is closed at its lower endbyya -cop:-" per or 'lead' allo'y disk -23 having *a diameter slight-i ;ilyle'ss thanthat of the target-suppor-tdefthe;

diskbeing'held in place'by'lugsg24 on the adjoining wall. The space between the target-support"? I9 and the disk-23 'is' 'covered?byianannular-X ray transparent windowr'25, convenientlyuaberyl lium ring." Thisring is inset into appropriates annular'grooves cut in the disk and;target-sup;-" port and is soldered in place; In this construc; tion the annular window, 25' is co-axialJwithLthe target 22*and spaced axially "therefrom and "has an efiective diameter less than that of the target.

Fitted over the lower end of the tube 3 is a tubular shield-support 26 which is integral with two lead-alloy shielding disks 21 and 28 each parallel to the plane of the target 22 and spaced axially therefrom and from each other. Annular slits 29 and 30 of limited width are cut in the shielding disks co-axial with the target 22, spider legs 3| being left to support the central portions of the disks. The diameters of the slits are chosen so that each is less than that of the window 25 and so that each slit is in the conical surface defined by the target 22 and the window slit 25, i. e. so that the slits are in the conical X-ray beam passing from the target through the window. In a preferred construction, the angle of the cone defined by the target 22, window 25 and slits 29 and 30 may be approximately degrees.

In practice, the tube 3 is constructed by conventional techniques and is exhausted and sealed ofi. In use, the anode it is grounded, a sufficient voltage is applied between the lead-wires to heat the filament l2 to incandescence, and a highvoltage is applied between the filament l2 and the anode 4. Under these conditions, electrons liberated at the filament escape the cathode structure through the opening i3 and impinge on the annular target 22, generating X-rays. These rays, although leaving the target in all directions, are for the most part absorbed in the shielding of the tube. However, those rays moving toward the annular window 25 pass through and leave the tube largely as a convergent beam. This X-ray beam is sharpened by the slits 29 and 30 in the shielding disks 21 and 28, which latter screen off radiation in all directions except that of the cone. The X-rays finally passing through the lower slit 30 are in the form of a hollow convergent cone and come to a fairly sharp focus, as shown in Fig. 3.

A typical use of the focused X-ray beam produced by the tube 3 is in deep X-ray therapy as illustrated in Fig. 3. For this purpose, the tube 3 is mounted on a horizontal supporting arm 32 secured to a vertical shaft 33 which may be rotated by a motor-and-gear-reducer 34 held by a support 35. The tube 3 is fixed to the arm 32 in a position tipped slightly in the plane of the arm 32 and shaft 33 to focus the convergent X-ray beam on a point beneath the center of the support 35. Then, when the shaft 33 is rotated, the X-ray tube 3 describes a circular path while maintaining the X-ray beam convergent on a fixed point.

In treating a region of deep-tissue 36 covered by overlying tissue 3'2, the tube 3 and support 35 are adjusted so that the focal point of the X-ray beam is within the region 35. The motor drive 34 is then energized to move the tube 3 in its circular path. The convergent beam of X-rays remains focused in the tissue 36, but the path of the beam through the overlying tissue is constantly changing. For this reason, and the further fact that the X-ray beam is hollow, no single portion of the overlying tissue receives more than a very minor fraction of the total X-ray dosage applied at the focal point. overexposure of the upper tissue is thus avoided.

It will be understood that the foregoing description is illustrative rather than limitative and that variations of the apparatus shown may be made within the scope of the following claims.

What is claimed is:

1. In a device for producin a beam of X-rays in the form of a hollow convergent cone, an X-ray tube having a cathode and an annular target, a shield spaced from the target parallel to the plane thereof and having therein an annular slit co-axial with the target and having a diameter less than that of the target, and a second shield parallel to the first at a point more remote from the target and having therein an annular slit co-axial with the target and having a diameter less than that of the first slit such as to be in the direct conical beam passing from the target through the first slit.

2. In a device for producing a beam of X-rays in the form of a hollow convergent cone comprising: an X-ray tube having a cathode, an annular target, and an annular X-ray window of diameter less than that of the target co-axial therewith and spaced axially therefrom; and a shield spaced axially from the window parallel to the plane of the target and having therein an annular slit co-axial with the target, the diameter of the slit being less than that of the window and such that the slit is in the direct conical X-ray beam passing from the target through the window.

3. In a device for producing a beam of X-rays in the form of a hollow convergent cone: an X-ray tube having a cathode, an annular target co-aXial with and spaced axially from the oathode and having its annular X-ray generating surface substantially parallel to the axis of the target, and an annular X-ray window of diameter less than that of the target co-axial therewith and spaced axially therefrom; and at least two shields spaced axially from the window and from each other, each parallel to the plane of the target and each having therein an annular slit coaxial with the target, the diameter of each slit being less than that of the window and such that the slit is in the direct conical X-ray beam passing from the target through the window.

4. A tube for producing a hollow conical beam of X-rays comprising a cathode, an annular target, and an X-ray opaque partition spaced axially from the target in the direction remote from the cathode and closing the tube, such partition having therein an annular X-ray transparent window co-axial with the target and of diameter less than the latter.

5. A tube according to claim 4 wherein the target is spaced axially from the cathode and has a cylindrical X-ray generating face parallel to the axis.

LUDO K. FREVEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,865,441 Mutscheller July 5, 1932 1,954,046 I-Ialberstadt Apr. 10, 1934 1,993,058 Hahn Mar. 5, 1935 2,167,114 Kieffer July 25, 1939 FOREIGN PATENTS Number Country Date 201,110 Germany Aug. '7, 1908 

